Pension and Other Postretirement Benefits (Details) (USD $) In Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Pension Benefits [Member]
Net periodic cost for pension and other postretirement benefits
Service cost	$ 1,006	$ 2,768	$ 3,072	$ 8,045
Interest cost	7,313	7,315	22,015	21,745
Expected return on plan assets	(8,541)	(8,298)	(25,692)	(24,692)
Plan net loss (gain)	1,599	3,094	4,810	9,248
Prior service cost (gain)	227	283	685	847
Transition obligation (asset)	(5)	(4)	(15)	(12)
Net curtailment/settlement loss (gain)	(165)		830	1,213
Net periodic benefit cost	1,434	5,158	5,705	16,394
Other Postretirement Benefits [Member]
Net periodic cost for pension and other postretirement benefits
Service cost	1	2	4	4
Interest cost	197	229	593	688
Plan net loss (gain)	27	(31)	81	(93)
Prior service cost (gain)	(63)	(63)	(189)	(189)
Transition obligation (asset)	192	192	575	575
Net periodic benefit cost	$ 354	$ 329	$ 1,064	$ 985